Auxiliary hydrostatic front wheel drive system

ABSTRACT

A vehicle such as a motor grader includes a hydrostatic auxiliary front wheel drive system which utilizes implement system pressurized fluid flow to drive a pair of fixed displacement hydraulic motors, such motors being drivingly connected to cause rotation of the front wheels. A pilot operated series-parallel valve in combination with a flow divider allows the motors to be driven in series or in parallel. A directional control valve is selectively responsive to operator control, and clutch actuation is accomplished automatically by directing a controlled portion of system fluid to such clutches to overcome the normal spring bias thereof.

BACKGROUND OF THE INVENTION

This invention relates to an auxiliary front wheel drive system for avehicle, and more particularly, to such a system which utilizesimplement system pressurized fluid flow for driving said front wheels.

Systems of the general type disclosed herein are shown in U.S. Pat. No.3,458,005 to Malm et al., U.S. Pat. No. 3,480,099 to Nighswonger et al.,and U.S. Pat. No. 3,481,419 to Kress et al. In such systems, a vehicleincludes motors for driving the front wheel thereof, such motors beingof the hydraulic type to be driven by fluid under pressure, in a seriesor parallel mode. Pressurized fluid supplied to each motor actuates aclutch associated with that motor so that a front wheel of the vehicleis drivingly engaged with the motor.

In any of the clutch engaging systems of these patents, it will be seenthat the fluid pressure to be applied to such clutch for engagementthereof may be directed from either the fluid conduit of the motorassociated with such clutch, or the fluid outlet conduit of such motor.While it will be seen that, in such situations, the higher of such twofluid pressures may be applied to the clutch for the engagement thereof,such clutch may in other situations be exposed to both the higher andlower pressures defined by such motor inlet and outlet conduits,resulting in a less than maximum fluid pressure being applied to suchclutch to actuate it.

In addition, in the area of such clutch in any of these three patents,no means are provided for preventing excessive pressure buildup in theclutch.

Of more general interest in this area are U.S. Pat. No. 2,818,699 toClemson, U.S. Pat. No. 3,153,908 to Lawrence, U.S. Pat. No. 3,184,994 toStahl, U.S. Pat. No. 3,186,506 to Leach, U.S. Pat. No. 3,255,840 toTangen, U.S. Pat. No. 3,272,576 to Budzich, U.S. Pat. No. 3,272,279 toBudzich, U.S. Pat. No. 3,302,741 to Brazuk, U.S. Pat. No. 3,354,977 toSwift, U.S. Pat. No. 3,391,753 to Anderson, U.S. Pat. No. 3,361,223 toBaver, U.S. Pat. No. 3,415,334 to Vriend, U.S. Pat. No. 3,469,648 toCannon, U.S. Pat. No. 3,447,547 to Kress et al., U.S. Pat. No. 3,493,067to Rumsey, U.S. Pat. No. 3,522,861 to Middlesworth et al., and U.S. Pat.No. 3,579,988 to Firth et al.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an auxiliary drive systemfor a vehicle which incorporate fluid motors and fluid pressure actuatedclutches which engage such motors with wheels of the vehicle, whereinthe fluid pressure actuated clutches are properly supplied with thehighest of the fluid pressures in the motor inlet and outlet means.

It is a further object of this invention to provide a system which,while fulfilling the above object, includes means for preventingexcessive fluid pressure buildup in such clutches.

It is a still further object of this invention to provide a systemwhich, while fulfilling the above objects, is simple in design andefficient in use.

Broadly stated, the invention is in a vehicle having a fluid motorassociated with a wheel thereof, and a fluid pump and a fluid supplyassociated therewith. Inlet conduit means connect the pump and motor forsupplying fluid under pressure from the pump to the motor, and outletconduit means extend from the motor, the fluid flowing from the motorthrough such outlet conduit means. The fluid passes through the motor todrive the motor. Clutch means are engageable upon an application offluid pressure thereto to effect a driving connection between the motorand wheel, and are disengageable to disconnect the motor and wheel. Theimprovement in such system comprises means for applying the greater ofthe fluid pressures in the inlet and outlet conduit means to the clutchmeans for inducing engagement thereof, and blocking the lesser of thefluid pressures in the inlet and outlet conduit means from the clutchmeans.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will become apparent from astudy of the following specification and drawings, in which:

FIG. 1 is a schematic illustration of a first embodiment of a frontwheel drive system of a vehicle; and

FIG. 2 is a schematic illustration of a second embodiment of a frontwheel drive system of the vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Shown in FIG. 1 is an auxiliary hydrostatic front wheel drive system foruse with the front wheels 90 of a vehicle (not shown). The vehicleincludes a main power source and rear wheels to be driven thereby, as iswell known. The main power source of the vehicle drives the pump 35which is utilized to operate the front wheel drive system of FIG. 1.

The operation of the combination of a motor 56, clutch 86, and wheel 90associated therewith, and also the combination of the motor 62, clutch86, and wheel 90 associated therewith, will be later described indetail. However, it should be understood that the motor 56 and clutch 86combination are mounted in fixed positions relative to each other, andare in turn pivotally mounted to an end of an axle (not shown) so as tobe pivotable relative thereto to allow changing of the attitude of thewheel 90 associated therewith, as is well-known. Likewise, the motor 62and clutch 86 combination are in fixed positions relative to each other,and are pivotally mounted to the opposite end of such axle (not shown)to allow changing of the attitude of the wheel 90 associated therewith.Appropriate well-known means may be utilized to interconnect thestructures associated with the ends of such axle so that the wheels 90of the vehicle may be moved to chosen pivotal attitudes, so that thevehicle may be steered. It is to be understood that the conduitsassociated with the motors 56,62 and clutches 86 are flexible so as toallow such proper turning of the wheels.

Referring to FIG. 1, reduced pilot pressure in a conduit 10 isselectively communicated to a three-position pilot operated forward andreverse valve 12 via solenoid operated pilot control valve 14 and 16,which are in communication with conduits 18 and 20, respectively.Reduced pressure is also supplied from conduit 10 to a solenoid operatedpilot control valve 22 which is selectively actuatable and permits thepilot signal to be communicated to control valve 24 and control valve 26via conduits 28 and 30 respectively. The solenoid operated controlvalves 14,16 and 22 receive an electrical signal for actuation thereofwhich corresponds to the ground speed of the vehicle. An electricalon/off switch, not shown, that is selectively controlled by theoperator, may block the current flow in lines 32, which places thesystem in its neutral condition when the front wheel drive is notrequired. When the vehicle transmission, not shown, is in the neutralposition, or the electrical switch described above is blocking lines 32,the solenoid operated pilot signal control valves 14,16 and 22 vent thepilot signal lines to tank 34.

To operate the front wheel drive system, the operator closes theelectrical switch described above, and shifts the vehicle transmissionto the first position, forward. An electrical signal is thencommunicated to solenoid operated pilot control valves 14 and 22 whichcommunicate pressurized fluid in conduit 10 to conduit 18, which shiftsthe forward and reverse control valve to its forward position "A." Pilotsignal pressure in conduit 10 is also communicated to conduit 28 andconduit 30 by control valve 22, which shifts control valve 24 andcontrol valve 26, respectively, to their second positions. Pressurizedfluid in the vehicle implement system which is supplied by a variabledisplacement pressure compensated pump 35 associated with a fluid supply37 is directed by a conduit 36 to a priority valve 38. Priority valve 38maintains a predetermined minimum pressure in the implement system. Whenthe pressure in conduit 36 is sufficient, priority valve 38 will shiftto communicate pressurized fluid to conduit 40 and through valve 12 toconduit 42. Control valve 26 in its shifted position communicates thefluid from conduit 42 to conduit 44 and through flow divider/combinervalve 46, which proportionally divides the flow and directs it byconduits 48 and 50 to control valve 24 which is shifted to its actuatedposition to communicate flow to conduits 52 and 54.

Conduit 52 connects to conduit 53 which in turn is connected to fixeddisplacement hydraulic motor 56, and conduit 54 is ultimately connectedto fixed displacement hydraulic motor 62 via conduits 58 and 60. Thepressurized inlet fluid entering the motors 56 and 62 via the above pathwill cause them to rotate. Conduits 61 as shown are motor case drainsand communicate motor leakage to tank 34. Outlet fluid from motor 56flows through conduit 64 and is directed back to tank via conduit 66,valve 26, conduit 68, conduit 70, valve 12 and conduit 72. A pilotoperated check valve 74 is normally open to tank during operation of thedrive motors 56,62, and will be discussed later in conjunction with theoperation of clutches associated with the motors 56,62. Fluid flowdischarged from motor 62 is directed to tank 34 via conduits 76,78,70,valve 12 and conduit 72.

As seen in FIG. 1, a conduit 81 communicates with conduits 52,53, aconduit 84 communicates with conduits 64,66 and a conduit 88communicates with a clutch 66, which is engageable upon application offluid pressure in the conduit 88 to effect a driving connection betweenmotor 56 and a wheel 90 of the vehicle. Likewise, a conduit 83communicates with conduits 58,60, a conduit 85 communicates withconduits 76,78, and a conduit 94 communicates with a clutch 86 which isengageable upon application of fluid pressure in the conduit 94 toeffect a driving connection between the motor 62 and a wheel 90 of thevehicle. These clutches are, of course, disengageable to disengage therespective motors and wheels.

A shuttle valve 80 connects conduits 81,84,88, so that the greater orhigher of the fluid pressure in the conduits 81 (motor inlet pressure)or 84 (motor outlet pressure) is directed into the conduit 88 to engagethe clutch 86, the shuttle valve 80 meanwhile blocking the lesser of thefluid pressures in conduits 81,84 from the conduit 88.

Likewise, a shuttle valve 92 connects conduits 83,85,94, and applies thegreatest or highest of fluid pressure in conduits 83,85 to engage theclutch 86, meanwhile blocking off the lower of the fluid pressures inconduits 83,85 from the clutch 86.

The pilot operated check valve 74 establishes the necessary backpressure in the system at startup to insure clutch actuation. Once thesystem is in operation, the pilot operated check valve 74 is unseated bypilot pressure in conduit 40 to permit free flow to tank 34.

The above description details the operation of the parallel flow conceptwhich establishes the low speed, high torque operation of the drivemotors 56,62.

When the vehicle transmission control is shifted to its second speedrange, the solenoid operated pilot signal valve 22 is vented to tank,which allows control valve 26 to shift back to its normal, or first orseries position, as shown in FIG. 1, and allows control valve 24 toshift to its deactuated position, also as shown in FIG. 1. Pilot signalvalve 14 remains actuated, and permits flow from the implement system topass through conduits 36,40 and 42 to control valve 26 and furtherthrough conduits 82 and 53 to motor 56. Outlet flow from motor 56 passesthrough conduits 64 and 66, through control valve 26, conduits 58 and 60and through motor 62, conduit 76, conduits 78 and 70, and through valve12 and conduit 72 to tank 34. Actuation of the clutches 86 is achievedin a manner similar to that previously described.

When the vehicle transmission control is shifted to the reverseposition, the solenoid operated pilot signal valve 16 communicatesreduced pilot pressure to valve 12 which shifts the valve 12 to itsposition "C" allowing implement system flow to be directed to the motorsin a direction opposite that previously described, and ultimately backto tank 34. Thus, inlet and outlet flows are reversed.

Referring to FIG. 2, this system is similar to that of FIG. 1 in that ituses the series-parallel flow concept and directional control valve toobtain two motor speeds in the forward direction and one motor speed inreverse. Clutch actuation in this system is achieved in a similar mannerin that it utilizes shuttle valves 80,92 to pick a higher systempressure for actuating the clutches 86 by means of conduits 91, 93,equivalent to conduits 88,94 of FIG. 1, through which fluid pressure issupplied to the clutches 86. However, pressure reducing valves 96 areincluded in conduits 91,93 to prevent excessive pressure buildup in theclutches 86. Such valves are exposed to fluid pressure in the conduits91,93 and will shift upon a level of pressure being achieved in conduits91,93 to prevent further pressure buildup in the clutches 86.

It is to be noted that, in order to achieve series drive of the motors,the control valve 98 is shifted into its first or series position (asshown in FIG. 2). Parallel drive of the motors is provided only with thecontrol valve 98 shifted into its second or parallel position, and thecontrol valve 100 shifted from its deactuated position (as shown in FIG.2) to its actuated position. (As set forth above, the system of FIG. 1is substantially the same in this area.) The shifting of the valves98,100 into such parallel and actuated conditions in the FIG. 2embodiment takes place upon application of fluid pressure which isoperatively associated with the valves 98,100 to so shift them upon acertain level of fluid pressure being achieved, the level of such fluidpressure being determined by the speed of the vehicle.

The forward and reverse valve 102 is manually actuated by the vehicleoperator to any one of its three selectively actuated positions.

What is claimed is:
 1. In a vehicle having a fluid motor associated witha wheel thereof, a fluid pump and a fluid supply associated therewith,inlet conduit means connecting the pump and motor for supplying fluidunder pressure from the pump to the motor, outlet conduit meansextending from the motor and through which fluid flows from the motor,the fluid passing through the motor to drive the motor, and clutch meansengageable upon application of fluid pressure thereto to effect adriving connection between the motor and wheel, and disengageable todisconnect the motor and wheel, the improvement which comprises meansfor applying the greater of the fluid pressures in the inlet and outletconduit means to the clutch means for inducing engagement thereof, andblocking the lesser of the fluid pressures in the inlet and outletconduit means from the clutch means.
 2. The apparatus of claim 1 whereinthe means for applying the greater of the fluid pressures in the inletand outlet conduit means to the clutch means and blocking the lesser ofthe fluid pressure in the inlet and outlet conduit means from the clutchmeans comprise a first conduit communicating with the inlet conduitmeans, a second conduit communicating with the outlet conduit means, athird conduit communicating with the clutch means and through whichfluid pressure may be applied to the clutch means to effect engagementthereof, and means connecting the first, second and third conduits fordirecting the greater of the fluid pressures in the first and secondconduits into the third conduit, and blocking the lesser of the fluidpressures in the first and second conduits from the fluid conduit. 3.The apparatus of claim 2 wherein the means connecting the first, secondand third conduits comprise shuttle valve means.
 4. The apparatus ofclaim 2 and further comprising means for preventing excessive fluidpressure buildup in the clutch means.
 5. The apparatus of claim 4wherein the means for preventing excessive fluid pressure buildup in theclutch means comprise valve means associated with the third conduit. 6.The apparatus of claim 3 and further comprising means for preventingexcessive fluid pressure buildup in the clutch means.
 7. The apparatusof claim 6 wherein the means for preventing excessive fluid pressurebuildup in the clutch means comprise valve means associated with thethird conduit.
 8. In a vehicle having a pair of wheels, a pair of fluidmotors associated therewith, means for transmitting power from themotors to drive the wheels, a fluid pump and a fluid supply associatedtherewith, and fluid circuit means operatively connecting the pump andthe motors, the improvement comprising control means operativelyassociated with the fluid circuit means comprising a first control valveshiftable into a first position, wherein the motors are connected withthe pump to be driven in series thereby, and into a second position,said control means further comprising a second control valve shiftableto an actuated position wherein, with the first control valve in itssecond position, the motors are connected with the pump to be driven inparallel thereby, the second control valve being shiftable to adeactuated position, said parallel drive being provided only with thefirst control valve in its second position and the second control valvein its actuated position, and further comprising means for shifting thefirst control valve to its second position and for shifting the secondcontrol valve to its actuated position, comprising fluid pressureoperatively associated with the first and second control valves to soshift said control valves to their second and actuated positionsrespectively upon a certain level of fluid pressure being achieved, thelevel of said fluid pressure being determined by the speed of thevehicle.